[leetcode][sort] H-Index

题目：

Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher's h-index.

According to the definition of h-index on Wikipedia: "A scientist has index h if h of his/her N papers have at least h citations each, and the other N − h papers have no more than h citations each."

For example, given citations = [3, 0, 6, 1, 5], which means the researcher has 5 papers in total and each of them had received 3, 0, 6, 1, 5 citations respectively. Since the researcher has 3 papers with at least 3 citations each and the remaining two with no more than 3 citations each, his h-index is 3.

Note: If there are several possible values for h, the maximum one is taken as the h-index.

方法一：

bool cmp(int a, int b){return a > b;}class Solution {public:int hIndex(vector<int>& citations) {if (citations.empty()) return 0;sort(citations.begin(), citations.end(), cmp);int res = 0;for (int i = 0; i < citations.size(); ++i){if (citations[i] > res) ++res;}return res;}};

方法二：

class Solution {public:int hIndex(vector<int>& citations) {if (citations.empty()) return 0;int n = citations.size();map<int, int> hashTable;int h = 0, cnt = 0;;for (int i = 0; i < n; ++i){map<int, int>::iterator iter = hashTable.find(citations[i]);if (iter != hashTable.end()) ++(iter->second);else hashTable.insert(make_pair(citations[i], 1));}for (map<int, int>::iterator iter = hashTable.begin(); iter != hashTable.end(); ++iter){int hNew = (n - cnt) < iter->first ? (n - cnt) : iter->first;if (h < hNew) h = hNew;cnt += iter->second;}return h;}};